The ring fortresses of Aggersborg, Fyrkat, Nonnebakken, Trelleborg and Borgring, constructed between about 970 and 980 CE during the reign of King Harald ‘Bluetooth’ Gormsson, represent outstanding examples and technological mastery of military architecture. Strategically positioned close to important land and sea routes across the Jutland peninsula and on the islands of Funen and Zealand in present-day Denmark, all five enclosures were constructed based on a uniform, precise, geometric, scalable design, and incorporated elements of natural topography for defensive purposes. The structures included fortified circular ramparts with four gateways located close to the cardinal points. In most cases, they were equipped with a concentric ditch, axial streets encircled by a ring street, and rows of longhouses geometrically arranged in the four quadrants of the fortified ring.
While functioning for only a brief period, this chain of Viking-Age fortresses is representative of the largest monuments that illustrate the centralisation of power by the Danish Jelling Dynasty and the consolidation of the kingdom of Denmark under King Harald, who integrated a vast territory spreading from present-day northern Germany to Denmark, southern Sweden and Norway. This network demonstrates the existence of a strong royal authority that was able, through military operations and alliance building, to command sufficient resources to exert sovereign control over territorial waters, land traffic and trade.
The fortresses, the function of which can only be inferred, testify to the early stages of state formation and socio-political transformations of the late 10th century CE in the Danish kingdom, including the conversion to Christianity, which eventually triggered the progression of statehood and Christianity in the whole of Scandinavia, and heralded the beginning of the Middle Ages in Northern Europe.
Criterion (iii): The monumental scale of the Viking-Age ring fortresses, built in a precise manner and within a single decade, signifies a high degree of centralised control and is evidence of King Harald’s ability to muster military power, resources and a local workforce to create a coherent system of surveillance and control over a vast territory. The ring fortresses testify to Harald’s state-building ambitions and can be seen as an outstanding testament of the process of state formation and an expression of a cultural shift in the geo-cultural context of Scandinavia and Northern Europe.
Criterion (iv): The chain of fortresses represents an outstanding example of monumental military architecture in Scandinavia and an exceptional integrated system within the wider context of the European Viking Age. The network demonstrates high technical values of construction and the exceptionality of a strictly ordered geometry in scalable form. The precise manner in which all five ring fortresses were built over a short period of time testifies to the existence of centralised power that was required to manage such a monumental infrastructure project involving resource-intensive engineering. Their strategic positioning linked to the control of major land and sea routes, and their territorial spread, hint at a unified system of governance over a vast area.
All the elements necessary to express the property’s Outstanding Universal Value are included within its boundaries. Archaeological deposits have been preserved at all five component parts sufficiently well to sustain the essential values of the property. The form of the excavated features survives intact in the subsoil. While the above-ground elements of the fortresses have suffered decay, the key structural elements of the Aggersborg, Fyrkat and Trelleborg enclosures are readable in the landscape. The Borgring and Nonnebakken fortresses are discernible only as small elevations, the latter being covered entirely by urban fabric. The landscape around the fortresses has changed substantially since the Viking Age due to natural and human-made factors. Elements of modern infrastructure have a visual impact on some of the individual component parts.
The original forms, designs, materials and substance of the ring fortresses have survived unaltered below ground at all five component parts, even in areas where archaeological excavations have taken place. The above-ground elements of the enclosures have been damaged due to various human activities and natural erosion over many centuries, and the landscapes of the five fortresses have evolved, but the strategic settings of the structures can still be comprehended. The five component parts contribute to the Outstanding Universal Value of the site as a whole, and the property does not suffer unduly from adverse effects of development and/or neglect.
Protection and management requirements
All five component parts are legally protected as ancient monuments at the national level through the Danish Museum Act (No. 1505 of 14 December 2006). At the municipal level, all of the fortresses are cited in the respective municipal plans, which are regulated by the Planning Act (No. 1027 of 20 October 2008). Spatial planning documents and special zoning restrictions provide additional protection to the property and the buffer zones.
The boundaries of the property reflect the highest level of national legal protection, with the exception of parts of Trelleborg and Borgring, where the process of extending the scheduled areas to cover the entire area of these component parts will depend on further archaeological investigations and negotiations with landowners. In these cases, the sections falling outside the scheduled areas are protected by compatible high-level nature protections.
Protection and management of the property reside at the highest level with the Danish Agency for Culture and Palaces. Management at the level of the component parts lies with the Danish Nature Agency at Aggersborg, the National Museum of Denmark at Fyrkat and Trelleborg, the Museum Southeast Denmark at Borgring, and the Odense City Museums at Nonnebakken. The management of the serial property will be coordinated by a Series Coordinator, responsible for the delivery of an integrated Property Management Plan (2023-2027) across all the component parts. A key mid- to long-term challenge will be to mitigate the negative visual impact modern infrastructure has on views to and from some of the component parts.